1. Field of the Invention
The present invention relates to an angular velocity detection element that detects an angular velocity using a Coriolis force. In particular, the present invention relates to an angular velocity detection element that causes a vibrating body to undergo driven vibration in an in-plane direction of a planar surface and detects an angular velocity based on a detection vibration generated in an in-plane direction or an out-of-plane direction by a Coriolis force.
2. Description of the Related Art
First, an example configuration of an angular velocity detection element of the related art will be described. Here, an axis that extends parallel to a direction (thickness direction) orthogonal to a planar surface of an angular velocity detection element including the planar surface is a Z axis of an orthogonal coordinates system. In addition, 2 axes that are parallel to the planar surface and orthogonal to each other are an X axis and a Y axis of the orthogonal coordinates system.
FIG. 16A is an X-Y plane plan view of an angular velocity detection element 201 according to a 1st example of the related art (for example, refer to Japanese Unexamined Patent Application Publication No. 2008-224628).
The angular velocity detection element 201 includes a support portion 202, arm portions 203A, 203B and 203C, piezoelectric functional layers 204A, 204B and 204C, a fixed portion 205 and a cushioning portion 206. The fixed portion 205, the cushioning portion 206, the support portion 202 and the arm portions 203A, 203B and 203C are integrated with one another. A surface of the fixed portion 205 on the negative direction side of the Z axis is joined to a support substrate, which is not illustrated. In addition, terminal electrodes electrically connected to the piezoelectric functional layers 204A, 204B and 204C, which will be described later, are provided on a surface of the fixed portion 205 on the positive direction side of the Z axis. The cushioning portion 206 extends in a positive Y axis direction from the fixed portion 205. A width of the cushioning portion 206 in an X axis direction is smaller than widths of the support portion 202 and the fixed portion 205. The support portion 202 extends in the positive Y axis direction from the cushioning portion 206. The arm portions 203A, 203B and 203C extend in the positive Y axis direction parallel to each other from the support portion 202. The cushioning portion 206, the support portion 202 and the arm portions 203A, 203B and 203C are supported by the fixed portion 205 as to float above the support substrate. The piezoelectric functional layers 204A, 204B and 204C are respectively provided on surfaces of the arm portions 203A, 203B and 203C on the positive direction side of the Z axis. The piezoelectric functional layers 204A and 204C have a function of exciting a driven vibration in the arm portions 203A, 203B and 203C. Specifically, the piezoelectric functional layers 204A and 204C expand and contract as a result of being input with a driving signal. The piezoelectric functional layers 204A and 204C expand and contract and as a result, the arm portions 203A and 203C undergo driven vibrations so as to bend in a Z axis direction. Driven vibrations are excited with the same phase in the arm portion 203A and the arm portion 203C. Thus, the arm portion 203B undergoes coupled vibration with the driven vibrations of the arm portions 203A and 203C and undergoes the same driven vibration along the Z axis. The driven vibration of the arm portion 203B and the driven vibrations of the arm portions 203A and 203C are excited with opposite phases. The piezoelectric functional layer 204B has a function of detecting a detection vibration of the arm portion 203B. In a state where the arm portion 203B is undergoing driven vibration, when an angular velocity acts around the Y axis, Coriolis forces are generated in the arm portions 203A, 203B and 203C and the arm portions 203A, 203B and 203C undergo detection vibration so as to bend in an X axis direction. The detection vibration of the arm portion 203B is detected via a piezoelectric effect of the piezoelectric functional layer 204B.
FIG. 16B is a perspective view of an angular velocity detection element 251 according to a 2nd example of the related art (for example, refer to Japanese Unexamined Patent Application Publication No. 2011-158319).
The angular velocity detection element 251 includes a base 252, detection beams 253A to 253D and a frame 256. The base 252 is positioned at the center of a planar surface of the angular velocity detection element 251. The detection beams 253A to 253D extend from the base 252 in a cross shape. One end of each of the detection beams 253A to 253D is connected to the base 252. The other end of each of the detection beams 253A to 253D is connected to the frame 256. The frame 256 has a substantially square shape when viewed in plan and is formed of corners 254A to 254D, which are positioned at the vertices of the substantially square shape, and driven beams 255A to 255D, which connect the corners 254A to 254D to each other. Masses 257A to 257D are attached to each of the driven beams 255A to 255D. The masses 257A to 257D are each formed of a pair of supplementary masses provided so as to sandwich the respective driven beams 255A to 255D therebetween. The pairs of supplementary masses forming the masses 257A to 257D are connected to the centers of the driven beams 255A to 255D.
Driving piezoelectric elements 260 to 263 are provided on surfaces of the driven beams 255A to 255D. The driving piezoelectric elements 260 to 263 are each formed of a pair of piezoelectric elements. The pair of piezoelectric elements forming each of the driving piezoelectric elements 260 to 263 are arranged parallel to each other along the directions in which the driven beams 255A to 255D extend. The driving piezoelectric elements 260 to 263 are applied with a driving voltage and as a result expand and contract. The driven beams 255A to 255D are driven by the driving piezoelectric elements 260 to 263 and undergo driven vibration so as to be alternately displaced in a direction toward the base 252 and in a direction away from the base 252 in the X-Y plane. The driven vibrations of the driven beams 255A to 255D are excited with the same phase.
Detection piezoelectric elements 264 to 267 are provided on surfaces of the detection beams 253A to 253D. The detection piezoelectric elements 264 to 267 are each formed of a pair of piezoelectric elements. The pair of piezoelectric elements forming each of the detection piezoelectric elements 264 to 267 are arranged parallel to each other along the directions in which the detection beams 253A to 253D extend. When an angular velocity acts on the angular velocity detection element 251, the detection beams 253A to 253D undergo detection vibration due to generated Coriolis forces. The detection piezoelectric elements 264 to 267 detect the detection vibrations of the detection beams 253A to 253D. More specifically, when an angular velocity acts on the angular velocity detection element 251 around a Z axis direction in a state where the driven beams 255A to 255D are undergoing driven vibration, Coriolis forces are generated in the masses 257A to 257D in a direction orthogonal to the direction in which the angular velocity is acting and orthogonal to the direction of the driven vibration. That is, Coriolis forces are generated in directions parallel to the directions in which the driven beams 255A to 255D extend in a state of rest. The masses 257A to 257D are displaced (undergo detection vibration) by the Coriolis forces. The detection vibrations of the masses 257A to 257D are transmitted to the detection beams 253A to 253D via the driven beams 255A to 255D and the corners 254A to 254D and the detection beams 253A to 253D are made to undergo detection vibration. The detection vibrations of the detection beams 253A to 253D are detected by the detection piezoelectric elements 264 to 267.
The above-described angular velocity detection element 201 is only able to detect an angular velocity around 1 axis and a plurality of the angular velocity detection elements 201 would have to be arranged along axes for which detection is desired in order to detect angular velocities around a plurality of axes. Consequently, there is a problem in that increases in package size and cost are incurred. In addition, since the arm portion 203B, on which the piezoelectric functional layer 204B to detect a detection vibration is provided, undergoes driven vibration in opposite directions along the Z axis to the arm portions 203A and 203C on either side, the piezoelectric functional layer 204B outputs a signal due to driven vibration even in a state where there is no angular velocity is acting. This signal could be removed by a circuit in a later stage but this would cause the detection sensitivity and detection accuracy of the angular velocity to be reduced.
Furthermore, the above-described angular velocity detection element 251 undergoes detection vibration such that all the masses rotate in the same direction around the Z axis when an angular velocity acts around the Z axis. Consequently, when an angular velocity acts around the Z axis, vibration of the weights acts as torque on the central base. Not limited to the case of an angular velocity around the Z axis, vibration of the weights similarly acts as torque on the central base in an out-of-plane direction when an angular velocity acts around the X axis or an angular velocity acts around the Y axis. That is, in the angular velocity detection element 251, there is a problem in that detection vibrations are not confined within the structure and escape and the detection beams are not able to be deform effectively and as a result the detection sensitivity is reduced. Furthermore, conversely, there is also a problem in that the above-mentioned detection vibrations may be generated by the effect of stress or vibration acting on the external structure and variations in characteristics may be caused by changes in temperature or changes in substrate stress, resulting in the detection accuracy being reduced.